In the agricultural industry, there is a need to kill weeds, insects, nematodes, bacteria and other single celled or multi-celled living organisms in the top soil of a field, for example immediately prior to growing crops. One common and effective agriculturally used disinfecting agent for treatment of top soil is methyl bromide. Methyl bromide effectively destroys living cells once methyl bromide is transported across the cell wall of a living organism. After the methyl bromide treatment, the top soil is conventionally used for growing plants such as crops.
However, methyl bromide is being phased out of agricultural use due to its deleterious effect on the ozone layer and due to its human health hazards. Thus a substitute for methyl bromide is urgently needed for killing undesirable living organisms commonly found in agricultural top soil suitable for plant growth purposes.
Ozone in aqueous solutions, hereinafter "aqueous ozone," has been used for inhibition or reduction of biological life forms such as molds, fungi, bacteria, algae, in numerous applications including swimming pools, potable water, bottled water, aquaria, fish hatcheries, and cooling towers. Ozone in the gas phase, hereinafter "gaseous ozone," has been used primarily in the food processing industries for sanitization of the surfaces of, for example, fish, grains, delicate vegetables, and processed foods. Gaseous ozone has also been used as a sanitizing agent for disinfecting the surfaces of operating rooms, animal containment facilities, and air conditioning and heating ventilation systems and for deodorization in municipal waste treatment plants.
Application of aqueous ozone to soil is not expected to be effective to kill living organisms because aqueous ozone has the drawback of slow dispersion of water into and through the soil of a field. Also, aqueous ozone suffers from rapid breakdown of ozone, so that maintaining sufficiently high concentrations of ozone in the water in the soil can be difficult. Aqueous ozone has a half life on the order of minutes in ambient conditions.
Although gaseous ozone has a half life on the order of hours (up to 20 hours depending on ambient conditions), according to traditional thinking, if gaseous ozone were used for soil treatment, ozone would quickly dissolve in the entrapped soil moisture and rapidly break down.
To increase stability of gaseous ozone in the soil environment, U.S. Pat. No. 5,269,943 to Wickramanayake suggests that "ozone containing gas is treated with acid" (abstract) and that "[a]fter the decontamination process, if the soil is found to be too acidic, the pH may be increased to the required level by applying unacidified gas ozone mixture for some time." (Col. 9, lines 65-68).
In treatment of surfaces of foods with aqueous ozone, virtually all of the surface dwelling living organisms are exposed to ozone. Furthermore, even for treatment of food surfaces using gaseous ozone, all the living organisms on food surfaces are exposed to predetermined, fixed concentrations of ozone. Conventional thinking suggests that gaseous ozone dispersion would be inhibited by the compacted, compressed nature of soil in a field or that untoward emissions of ozone gas would escape from the soil in a field into the atmosphere and so minimize ozone's effectiveness.
Traditional thinking also indicated difficultly in maintaining sufficiently high concentrations of gaseous ozone in soil for the periods of time necessary to kill the living organisms that may be harbored and/or partially protected in either pores of individual soil particles or in the interstitial spaces in clumps of soil. Moreover, living organisms in soil can exist in cyst-like states during extended periods of seasonal dormancy, and so become resistant to many types of biocidal treatments.
Traditional thinking also indicated that the sometimes high concentration of naturally occurring organic compounds in soil close to the surface of a field can consume large amounts of ozone and so result in insufficient exposure of living organisms in the soil to ozone.